In a decision that could have implications nationally and in Wisconsin's November elections, a federal judge on Tuesday struck down the state's voter ID law, saying it violated the Voting Rights Act and the U.S. Constitution.

The law known as Act 23 had already been blocked by a state judge. For the law to be put back in place, supporters would have to overturn both the state and federal decisions — a possibility thatcould prove difficult between now and the Nov. 4 election for governor.

"There is no way to determine exactly how many people Act 23 will prevent or deter from voting without considering the individual circumstances of each of the 300,000 plus citizens who lack an ID," U.S. District Judge Lynn Adelman wrote in his 70-page ruling. "But no matter how imprecise my estimate may be, it is absolutely clear that Act 23 will prevent more legitimate votes from being cast than fraudulent votes."

Adelman, who is based in Milwaukee, found the state didn't have an appropriate rationale for imposing a voter ID requirement. In-person voter impersonation — the only type of fraud a voter ID law can prevent — is nonexistent or virtually nonexistent in Wisconsin, he wrote.

"Because virtually no voter impersonation occurs in Wisconsin and it is exceedingly unlikely that voter impersonation will become a problem in Wisconsin in the foreseeable future, this particular state interest has very little weight," he wrote.

"The defendants could not point to a single instance of known voter impersonation occurring in Wisconsin at any time in the recent past."

Adelman, a former Democratic state senator known for sponsoring the state's open records law, determined that in practice the law requiring voters to show one of nine types of photo IDs at the polls established an unconstitutional burden on the right to vote. It also violated the federal Voting Rights Act because its effects hit Latinos and African-Americans harder than whites, he wrote.

Under the voter ID law, minorities "must pay the cost, in the form of time or bother or out-of-pocket expense, to obtain what is essentially a license to vote," he wrote.

He issued an injunction barring the voter ID law from being enforced.

State Attorney General J.B. Van Hollen, who defended the law, immediately pledged to take the case to the 7th Circuit Court of Appeals in Chicago.

"I am disappointed with the order and continue to believe Wisconsin's law is constitutional. We will appeal," Van Hollen, a Republican, said in a statement.

Van Hollen spokeswoman Dana Brueck didn't address whether the attorney general would seek to expedite the appeal, saying simply that he would work to "get it back on the books as soon as possible."

A lawyer for the American Civil Liberties Union of Wisconsin — one of the many groups that brought the challenge — praised the ruling, calling it a victory for the minority witnesses who came forward to explain how the law would prevent them from voting in Wisconsin as they had in the past. The plaintiffs represented by the ACLU included Shirley Brown, an African-American woman in her 70s who said she was born at home in Louisiana and never had a birth certificate.

"We are very pleased that the judge recognized what we believe we showed at trial, which is that Wisconsin's voter ID law did have a discriminatory effect on African-American and Latino voters," said Karyn Rotker, a senior attorney for the state ACLU.

Dale Ho, director of the national ACLU's voting rights project, said he expected the decision to be a "bellwether" as federal courts consider challenges in Texas and North Carolina.

In March, GOP Gov. Scott Walker said he would call a special legislative session on voter ID this spring or summer if the courts ruled against the requirement. Spokeswoman Laurel Patrick said the governor believes the law is "constitutional and will ultimately be upheld."

"We're reviewing the decision for any potential action," Patrick said.

Walker faces Democrat Mary Burke in November.

Speaking to reporters Tuesday, Assembly Speaker Robin Vos (R-Rochester) said he hoped lawmakers would take up fixes to the photo ID law that were passed by the Assembly in November but not taken up by the Senate.

Those changes, designed to comply with the earlier state court ruling, would allow voters to cast a ballot without a photo ID if they signed sworn statements saying they were poor and could not obtain a photo ID without paying a fee, had a religious objection to being photographed or could not obtain birth certificates or other documentation necessary to get a photo ID.

Senate Majority Leader Scott Fitzgerald (R-Juneau) said Republicans in his house are committed to photo ID and would "review our options" in light of the Adelman ruling and any state Supreme Court decisions.

Lawmakers ended their regular session this month. To take up voter ID changes, Walker or legislative leaders would have to call the Legislature back into session.

In his ruling, Adelman laid out a process for considering any action taken by lawmakers to fix the flaws he identified. He said he would hold expedited hearings on whether any amendments to the law would be legal and could be enforced at the next election.

"However, I also note that, given the evidence presented at trial showing that blacks and Latinos are more likely than whites to lack an ID, it is difficult to see how an amendment to the photo ID requirement could remove its disproportionate racial impact and discriminatory result," he wrote.

Vos said he would review the federal decision but so far saw little reason to respond to it, saying that Adelman acted as if he were still a lawmaker rather than a judge.

"What's the point of that? He's already said there's almost no circumstances under which I could find it constitutional because he starts with a heavy liberal bias and not that of a judge," Vos said.

Vos said Republicans had tried to accommodate critics by allowing people to get free state-issued IDs. But Adelman found too many barriers remained for those who didn't have IDs; for instance, under the voter ID law, people still have to pay a fee to get copies of their birth certificates, which are necessary for the free IDs.

Adelman wrote one would have to be "insane" to commit voter fraud because the penalties are so stiff and the gain so small. "The potential costs of perpetrating the fraud, which include a $10,000 fine and three years of imprisonment, are extremely high in comparison to the potential benefits, which would be nothing more than one additional vote for a preferred candidate (or one fewer vote for an opposing candidate), a vote which is unlikely to change the election's outcome," he wrote.

Evidence showed impersonation fraud is essentially nonexistent, he determined. Testimony from a prosecutor in the case at the most shows only that "cases of potential voter-impersonation fraud occur so infrequently that no rational person familiar with the relevant facts could be concerned about them," Adelman wrote.

Walker and his fellow Republicans in the Legislature approved the voter ID law in 2011, as a host of other states were passing similar laws.

The U.S. Supreme Court in 2008 ruled Indiana's voter ID law was constitutional, but many of the laws passed since then — including Wisconsin's — are more restrictive and have faced legal challenges. They continue to work their way through the courts and the nation's high court is expected to eventually revisit the issue.

In Wisconsin, the voter ID law was in place for the low-turnout February 2012 primary, but then struck down by two Dane County judges. An appeals court overruled one of the Dane County decisions, but the other ruling remains in place.

The state Supreme Court is now considering both those cases and is expected to rule by this summer. During arguments in the cases in February, some members of the court — including one of the conservatives who control the court — raised concerns about aspects of the voter ID requirement.

Adelman's ruling deals with two challenges, brought in federal court. He heard the cases together and issued a single decision because they shared similar elements.

In the federal cases, those suing include the ACLU, Cross Lutheran Church, labor unions and the Wisconsin chapter of the League of United Latin American Citizens.

Even if the state Supreme Court finds the voter ID law is in keeping with the state constitution, the law will remain blocked by the federal court.

Attorney Lester Pines of Madison said he was still digesting the federal court's decision but emphasized that the state litigation remains important. Pines represents the League of Women Voters of Wisconsin, which brought one of the two challenges to the law in state court.

"The Wisconsin Supreme Court on its own can decide and probably should decide whether the current voter ID law violates the Wisconsin constitution," Pines said. "There's still a live case before the Wisconsin Supreme Court."

In the federal appeal, Pines said it could take months for the appeals briefs to be filed, oral arguments made and a decision rendered by the appeals court. That means that it would be difficult, though not impossible, for a federal appeals court to issue a decision before November's election, he said.

Milwaukee Mayor Tom Barrett — a Democrat who ran against Walker in 2010 and in a 2012 recall election — praised the decision.

"I want people who are legally eligible to vote to be able to vote without restrictions," he said.

Don Walker of the Journal Sentinel staff contributed to this report.

What's next

■ Attorney General J.B. Van Hollen said he would appeal the ruling striking down the voter ID law.

■ The state Supreme Court is already considering two other challenges to the law and is expected to rule by summer. To be reinstated, the voter ID law would have to overcome all legal challenges, in both state and federal court.

■ Republicans who control state government may hold a special legislative session to pass a voter ID statute more likely to pass court muster. That could be quickly reviewed by U.S. District Judge Lynn Adelman, who issued Tuesday's decision.

About Patrick Marley

Patrick Marley covers state government and state politics. He is the author, with Journal Sentinel reporter Jason Stein, of "More Than They Bargained For: Scott Walker, Unions and the Fight for Wisconsin.”

About Jason Stein

Jason Stein covers the state Capitol and is the author with his colleague Patrick Marley of "More than They Bargained For: Scott Walker, Unions and the Fight for Wisconsin." His work has been recognized by journalism groups such as the American Society of News Editors, the Society of American Business Editors and Writers, and the Association of Capitol Reporters and Editors.